Currently, DVFS technology has been widely used in various processors, and the DVFS technology is capable of efficiently managing power consumption of an electronic system. The challenge for using the DVFS technology is to determine which operating frequency to use because the operating voltage is also determined by the operating frequency accordingly. The electronic system may have lower power consumption when the operating frequency and operating voltage have been lowered. Conventional DVFS technologies utilize a processor to calibrate the operating frequency and operating voltage by software, and cannot respond to real-time conditions. There is also extra overhead for the software. Accordingly, there is a demand for a DVFS system and associated DVFS method to solve the aforementioned issues in conventional DVFS technologies.